The 423-carat (85 g) blue Logan Sapphire
|Aluminium oxide, Al2O3|
|Crystal class||Hexagonal scalenohedral (3m) |
H-M symbol: (32/m)
|Color||Typically blue, but varies|
|Crystal habit||As crystals, massive and granular|
|Mohs scale hardness||9.0|
|Optical properties||Abbe number 72.2|
|Refractive index||nω=1.768–1.772 |
|Melting point||2,030–2,050 °C|
|Other characteristics||Coefficient of thermal expansion (5.0–6.6)×10−6/K |
relative permittivity at 20 °C
ε = 8.9–11.1 (anisotropic)
Sapphire is a precious gemstone and a variety of the mineral corundum (α-Al2O3), It is usually blue, but natural "fancy" sapphires also occur in all other colors other than red as red colored corundum is called ruby. The variety in color is due to small amounts of elements such as iron, titanium, chromium, copper, or magnesium mixed in.
- Harman, Alang Kasim; Ninomiya, Susumu; Adachi, Sadao (1994). "Optical constants of sapphire (alpha-Al2O3) single crystals". Journal of Applied Physics 76 (12): 8032–8036. Bibcode 1994JAP....76.8032H. doi:10.1063/1.357922.
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